Miscellaneous Intelligence. 323 



stone, some bands will be more argillaceous, siliceous, ferriferous, 

 or magnesian, or two or more of these impurities may abound, so 

 that in a stratified rock of this kind, the minerals developed in 

 one band will differ from those in another, as is so strikingly 

 shown in specimen No. 41. 



" This metamorphism is selective only in the early stages, for 

 (as in 36, 54, and 40) we have the silicate bands encroaching 

 upon the inte'rvening marble strata ; whilst in 44, the well strati- 

 fied portion, toward the metamorphosing focus, is fused (?) up 

 into a fairly homogeneous mass of coarser grains and larger crys- 

 tals of the same minerals as in the undisturbed part, together 

 with the addition of others. Yet that the composition of the 

 bands has a strong determining influence on the results is well 

 illustrated in No. 51. 



" The order in which the new minerals seem to develop is the 

 following : 



(1) Peridote, Periclase, Humite. 



(2) Spinel, Mica, Fluorite, Galena, Pyrites, Wollastonite. 



(3) Garnet, Idocrase, Nepheline, Sodalite, Feldspar. 



(4) Calcite (secondary). 



"Although in some cases there is an approach to the order of 

 mineral species found in the druse walls described by Mierisch 

 (loc. cit. p. 121), yet these are exceptional, and open up for oar 

 investigation a far wider field of facts. 



"It is evident that any researches as to the purely chemical 

 changes that take place in the process of metamorphism would 

 be useless in stratified limestones unless it were possible to know 

 the composition of each band. It will therefore be better to con- 

 sider these questions where treating of the massive limestones 

 and their derivatives. 



"Then also, it is necessary to study the changes that have 

 taken place in the minerals originally replacing the limestone. 

 We have distinct evidence of the conversion of periclase into 

 brucite, and of peridote to a whitish fibrous mineral or pilite (?) 

 The biotite, nephelene, feldspar (?) and peridote may be crowded 

 with microliths, which there is good reason to believe consist of 

 pyroxene. 



"Another point of interest is that I have not so far noticed the 

 presence of periclase in any rock where graphite could be de- 

 tected. This might well be explained by the fact that so long as 

 free carbon remained, the magnesia would be maintained as car- 

 bonate, and only on its loss of the C0 2 could it take up the Si0 2 

 to form fosterite, or, with the addition of lime, monticellite ; or 

 should silica be absent, to combine with any alumina and to 

 separate as spinel. 



"Specimen 51 indicates, at any rate, that the latter result is 

 subsequent to the former. Certainly 200 is curious, as showing 

 an apparent displacement of the carbon grains by peridote, 

 although it may be that that mineral simply occupies the spaces 

 left by the disappearing carbon. 



